We’ve all heard the argument that if we’re going to “feed the world”—sustain the 9 billion human beings expected to populate the earth by 2050—we’d better find a way to grow more food. Often, that’s an argument made to promote yield-intensive methods of big agribusiness: machination, automation, synthetic fertilization, genetic modification. But a peer-reviewed study in this month’s Science, a special Earth Day issue devoted to sustaining the global ecosystem, makes a different case. We can’t just grow more, the authors claim. We have to eat less, too.

The solution they suggest isn’t a scientific one—breeding new nutrient-dense hybrids, say, or getting ascetic quick by CRISPRing out our hunger genes. Their argument has no obvious link to food: the first step towards sustainably feeding the world, they say, should be to empower women and girls worldwide.

Population control doesn’t have to mean denying the humanity of others. It can be about empowering people—and must be, if we’re going to endure the challenges ahead.

But first, why isn’t it enough to simply grow more food? The study suggests that it’s naïve to think our problem is only about scaling up agriculture sufficiently to fill 9 billion bellies, because of the massive ecological toll that agriculture takes on the planet’s ecology. We need food to survive, but we need more than food alone. Clean water, healthy pollinators, and stable climate are also essential to our survival. Biodiversity tends to promote these factors. Agriculture tends to do the opposite. Our challenge is to grow more food while at the same time maintaining existing ecosystems—what’s known as “sustainable intensification.” That will be difficult, and it may not be enough.

“Ongoing tropical deforestation, anticipated expansion of cultivated areas, a projected 55% increase in demand for water by 2050, expected growth in global pesticide use, the steady increase of greenhouse gases (with agriculture a major contributor), and the expansion of global trade of food and other products all foreshadow a mounting impact of food production,” the authors write. “It appears questionable whether sustainable intensification can prevail over biodiversity-encroaching food production trends.”

That’s a problem that we can’t just solve with higher yields. It’s not just a supply-side issue, in other words. It’s a demand-side issue, too. We simply must consume less. And that, the authors argue, means finding ways to substantially reduce the rate of population growth.

The crucial policies are prioritizing education for girls and women, making family planning accessible and affordable, ensuring broad access to contraceptives, providing counseling for couples, and making sex ed mandatory in schools.

That’s where things get tricky. Theories of population control obviously have a fraught history, including violent coercive measures like China’s “one-child” policy and hateful ideologies that pin the world’s ills on the reproductive habits of the poor. The study acknowledges that this backdrop has hindered research on this topic, and is yet another force driving the incessant focus on maximizing production. Still, the authors argue, population control doesn’t have to mean denying the humanity of others. It can be about empowering people—and must be, if we’re going to endure the challenges ahead.

The good news is that population control doesn’t have to be a form of coercion. In societies where women are equitably treated, population growth seems to slows organically, and dramatically. Prioritizing urgently-needed human rights has the additional benefit, in other words, of reducing our demands upon the earth. And this amounts to a win-win.

“Ensuring educational opportunities for girls and women can move the world more swiftly toward a smaller population,” the authors write. “Indeed, achieving full gender equality would, in all likelihood lead to global fertility below—and possibly well below—the replacement value of roughly 2.1 children.”

The study offers a powerful example. In Africa, women with no education average 5.4 children, but only 4.3 children if they’ve completed primary school. Those who complete secondary school average only 2.7 children, while those who go on to college average only 2.2 children. Perhaps even more striking is this statistic: in the Americas, more than one out of every two pregnancies is unplanned.

The crucial policies are prioritizing education for girls and women, making family planning accessible and affordable, ensuring broad access to contraceptives, providing counseling for couples, and making sex ed mandatory in schools. “Wherever human-rights-promoting policies to lower fertility rates have been implemented, birth rates have declined within a generation or two,” the authors write.

There’s another problem with the “grow more food, feed the world” line of thinking, one the study doesn’t address directly: agricultural output matters less in places where can’t find or afford food, and distribution is very sensitive to political realities. Three of the four nations currently on the verge of famine grow enough to feed themselves (Yemen is the exception); in each case, conflict has created false scarcity. Where injustice goes, hunger follows—no matter how much food we grow, and no matter how sophisticated our technology becomes.

That’s why feeding the world isn’t going to start in a lab somewhere. It’s going to start by looking at the underlying causes of systemic injustice, and undertaking the hard work of correcting them. Turns out that, by doing so, we just might save the planet, too.